Method of inhibiting corrosion of ferrous metal surfaces



METHOD F INHIBITING CORROSION OF FERROU METAL SURFACES N0 Drawing; Application June 24,1954

Serial No. 439,158

'Claims. (Cl.252--8.55)

This invention relates to an improved method of inhibiting corrosion of ferrous metals and particularly the terrous metal equipment associated with the production of petroleum hydrocarbons, as in a producing oil well. Additionally, the invention relates to an improved arsenical composition which is adapted for aqueous dilution and suitable for application as a corrosion inhibitor for ferrous metals and particularly as an inhibitor for carbon dioxide-inducedmetal corrosion.

Ferrous metal corrosion has long been recognized as one of the most serious problems associated with the production and recovery of petroleum hydrocarbons from subsurface formations. The corrosive attack upon the ferrous metal surfaces in contact with the production fluid is primarily due to the action of the weak acidic solutions, such as the aqueous solutions of carbon dioxide, normally present in the production fluid. While the presence of the carbonic acid solutions PI'ESUH'ICSZIII acid attack upon the ferrous metal surfaces, other integral and contributing corrosive actions have been recognized. Thus, electrochemical corrosive action is also a major factor.

Although numerous chemical inhibitors have been previously proposed for the treatment of ferrous metal sur faces in contact with corrosive well fluids, it is only recently that any measure of success has been obtained in the practical solution of this problem. It has recently been proposed to inject into the production fluid and circulate throughout the production system an arsenical composition comprising the alkali metal arsenites or alkaline solutions of arsenious oxide. These alkaline arsenical compositions have been used successfully both in the form of dilute aqueous solutions which are pumped or lubricated, intermittently or continuously, into a producing well, or in the form of solid compositions which are dropped into the production tubing and gradually are dissolved into the production fluid. These arsenical corrosion inhibitors provided a tenacious protective film upon the ferrous metal surfaces which successfully inhibits the corrosive action of the contacting production fluid.

In the practical or field application of these alkaline arsenical inhibitors, certain difilculties have been encountered which have prevented the full utilization of the arsenious oxide content of the inhibitor. It has been found that under certain conditions the alkaline arsenicals will form deposits in the form of flocculent precipitates and sludges in the dilution tanks and throughout the injection system associated with the introduction of the inhibitor into a producing oil well.

Basically, in order to achieve a water-soluble, highlyconcentrated formulation of arsenious oxide (at least 2 pounds As O per gallon), it is necessary to employ a high alkali-arsenic ratio in the formulations. When employing hard waters of at least 70 p. p. m. for dilution in the field mixing tanks, it is noted that deposits are formed throughout the inhibitor system which are largely composed of compounds containing the alkaline earth and heavy metal cations of the dilution water. In extrernely hard waters (several hundred p. p. m.), precipitaiii Fatented Feb. it 'lfiSQ 2 tion and sludge deposition are almost immediate and voluminous.

Another contributing factor to the formation of tie posits on dilution of the alkaline arsenical inhibitors is the presence of antimony impurities associated with the arsenic. Generally, the commercial grades of arsenious oxide contain about 1 to 3 percent of the oxides of antimony and, in the preparation of the alkaline arsenical inhibitors, the conditions of reaction are conducive to the solution of the oxides of antimony with the arsenious oxide. On dilution, irrespective of the hardness of the diluting water, the very low solubility of Sb O is approached and the metal surfaces of the tanks, pumps and piping become coated with a sludge high in antimony.

A typical analysis of such a coatingis as follows:

Tank Valve Deposit Deposit Percent Percent In contrast to the foregoing difliculties in field application of the alkaline arsenical corrosion inhibitors, it has now been found possible to provide a water-miscible arsenical corrosion inhibitor which may be formulated as a concentrate containing at least 2 pounds of As O per gallon which is stable in storage; contains negligible quantities of antimony oxides; on dilution with waters having a hardness greater than 70 p. p. m., will not precipitate the alkaline earth and heavy metal cations; and, in general, provides deposit-free operation as a corrosion inhibitor for ferrous metals and particularly the ferrous metal equipment associated with the production of petroleum hydrocarbons.

In accordance with the present invention, it has been discovered that the water-miscible reaction products of arsenious oxide and polyhydric alcohols will provide an arsenical corrosion inhibitor for ferrous metals which ossesses materially improved performance characteristics and more universal application over the conventional alkaline arsenical compositions. Although these reaction products result in the formation of arsenite esters, these esters are not necessarily the sole component of the reac tion product, which more than likely consists of a mixture of esters and dissolved arsenious oxide.

The properties of the reaction product will vary' according to "the type of polyhydric alcohol and the mol ratio of reactants employed. The reaction products may vary from a water-miscible, low-viscosity liquid product to a water-miscible, solid or glass-like product. Generally, in order to provide a reaction product possessing op timum water-miscibility and a lower viscosity, it is proferred, to react the polyhydric alcohol at such a mol ratio as to provide at least one free hydroxyl group available in the reaction product.

The types of polyhydric alcohols which have been found suitable in the preparation of the arsenical reaction products'may be classified into the normally-liquid polyhydroxy aliphatic compounds and the normally-solid polyhydroxy aliphatic compounds. The preferred mol ratios of reactants to produce a stable, water-miscible corrosion inhibitor will lie within the range of 1 mol of arsenious oxide to from 3 to- 8 mols of the normally-liquid polyhydric alcohols, and in the range of 1 mol of arsenious oxide to 0.5 to 4 mols of normally-solidpolyhydric alcohols. a

In the case of the reaction products obtained from the reaction of the normally-solid polyhydric alcohols, as represented by pentaterythritol, the reaction will result in a water-miscible, glass-like reaction product which is eminently suited as a solid arsenical corrosion inhibitor which may be introduced into a producing well in the form of a molded stick and is gradually dissolved in the production fluid to provide corrosion inhibition to the ferrous metal surfaces in contact with the production fluid. An additional advantage of the'pentaterythritol arsenical composition is the fact that under ccrtain'conditions of operation the solid inhibitor will gradually decompose and release formaldehyde which will aflord additional hydrogen sulfide corrosion protection.

Of the normally-liquid polyhydric alcohols, the dihydric alcohols or the glycols containing from 2 to 4 carbon atoms are the most desirable. The glycols, when reacted with arsenious oxide in the mol ratio range of from 3 to 8 mols of glycol per mol of arsenious oxide, will result in a stable, Water-miscible, free-flowing product whichis readily compounded in concentrations of at least 4 pounds of AS203 per gallon, and may be diluted Without deposit formation at the conventional field dilutions of 1 to 30 or greater.

The reaction of the polyhydric alcohols and the arsenous oxide to form the arsenical corrosion inhibitor of the invention inherently avoids the presence of normallyassociated antimony in the I reaction product. H Under the conditions of the reaction, the oxides of antimony do not esterify with the polyhydric alcohols, and theantirnony is substantially eliminated in the reaction residue or sludge. In general, the reaction is conducted by heating the reactants together in the presence of catalytic amounts of a condensing agent, such as about 0.01 to 0.5 percent by weight of a strong mineral acid or a strong base, at atemperature. of at least 100 C. and below the boiling point of the polyhydric alcohols. At temperatures approaching 100i. C .,.'the reaction is exothermic and-proceeds rapidly with the elimination of water. Upon comple tion of the reaction, the reaction productv is immediately applicableas an arsenicalcorrosion inhibitor. T

A number of variations have been employed. in carrying out the reaction which may find practical application. Thus, an entraining solvent may be incorporated in the reaction to remove the water formed, and therebylallow a greater control of reaction temperatures. Preparations havebeen madeinthc absence of a condensing agent, but such reactions require prolonged heating ofthe reaction mass in order to complete removal of the reaction Water. v The following example is presented as .an illustration of the details of the invention.

Example 7 The reaction mass was heated and, as the temperature approached 100 C., catalytic amounts 'of 50 percent caustic were added. An instantaneous 'exotherrni'o'reaction occurred. The reaction temperature was controlled so that it remained below the boiling point of the propylene glycol. Steam was driven off, and the reaction mass was stirred for to 10 minutes and then cooled. The resulting reaction product was clear, water-white, slightly viscous, but flowable, and water-miscible. When diluted to a l to 40 dilution, it did not precipitate either in hard water or when carbon dioxide was bubbled through the solution. When employing technical-grade arsenious oxide containing about 1 to 3 percent of the oxides of antimony, the reaction product is separated from the reaction sludge in which substantially all of the antimony is present.

Additional preparations were conducted employing a condensing system on the reaction vessel whereby the reaction temperature was controlled to allow the water to escape and refluxing the glycol.

Additional preparations were conducted with ethylene glycol, glycerol, 70 percent commercial sorbitol, percent invert sugar glucose, and pentaerythritol with varying mol ratios to produce stable, water-miscible arsenical corrosion inhibitors which, when evaluated for corrosion inhibition according to the test procedure of Scott and Rohrback published in Corrosion, vol. 8, No. 7, pages 234-239, July 1952, showed at least 85 percent corrosion inhibition of ferrous metal surfaces.

Obviously, many modifications and variations of the invention, as hereinbe fore set forth,'may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

I claim: v 1. -A method of inhibitingthe corrosion of ferrous metals subject to contact with aqueous solutions of car bon dioxidewhich comprises introducing into contact with said ferrous metals a water-miscible reaction productof As O and a polyhydric alcohol obtained'at reaction 'te'rnper'atures of at least about C. and below the boilingp'oint of said polyhydric alcohol, said reaction product containing at least one free hydroxyl radical.

2. A method of inhibiting corrosion'of ferrous metals which comprises introducing into contactwith said ferrous metals a water-miscible reaction product of arsenious oxide and a dihydric alcohol containing from 2 to 4 carbon atoms, said reaction product being obtained bythe reaction'of 1 mol of arsenious oxide for every3 to' 8 mols of said dihydric alcohol and at'reaction temperatures of atleast about 100 C. and below'th'e boiling point of said dihydric alcohol.

, 3. A stable arsenrcal composition comprising a watermiscible reaction product of arsenious oxide and 21 nor mally-solid polyhydric'alcohol obtained by the reaction of 1 mol of arsenious oxide to 0.5 to 4 mols of the normally-solid polyhydric alcohol at reaction temperatures of at least 100 C. and below the boiling point of said polyhydric alcohol. a

4. A solid arsenical corrosion inhibitor suitable for gradual solution in the production fluid of a producing oil well which comprises a water-miscible reaction product of arseniousfoxide and 'pentaerythritol, said reaction product being obtained by the reaction of 1 mol of arsenious oxide for every 0.5 to 4 mols of pentaerythri tol and at reaction temperatures of at least 100 C. and below the boiling point of pentaerythritol.

5. 'A method of inhibit'ng the corrosion of ferrous metals which comprises introducing into contact with said ferrous metals a water-miscible reaction product of arsenious oxide and a polyhydric alcohol obtained by the r'eaction'of arsenious oxide with a polyhydric alcohol atreaction'te'mperatures of at least 100 C. and below the boiling point of said polyhydric alcohol and at mol ratios such that said reaction product contains at least one free hydroxyl radical.

' References Cited in the file of this patent .UNITED STATES PATENTS 20,665/34- Australia a Aug. 21, 1935 

1. A METHOD OF INHIBITING THE CORROSION OF FERROUS METALS SUBJEC TO CONTACT WITH AQUEOUS SOLUTIONS OF CARBON DIOXIDE WHICH COMPRISES INTRODUNCING INTO CONTACT WITH SAID FERROUS METALS A WATER-SOLUBLE REACTION PRODUCT OF AS2O3 AND A POLYHYDRIC ALCOHOL OBTAINED AT REACTION TEMPERATURES OF AT LEAST ABOUT 100*C. AND BELOW THE BOILING POINT OF SAID POLYHYDRIC ALCOHOL, SAID REACTION PRODUCT CONTAINING AT LEAST ONE FREE HYDROXYL RADICAL. 